Devil: an IDL for Hardware Programming

Transcription

1 Devil: an IDL for Hardware Programming Fabrice Mérillon, Laurent Réveillère, Charles Consel, Renaud Marlet, Gilles Muller Group Irisa/Labri, Rennes/Bordeaux (France) 1

2 Interfacing Devices... The Devil is in the details 2 2

3 Looking into the "Details" #define MSE_DATA_PORT #define MSE_SIGNATURE_PORT #define MSE_CONTROL_PORT... #define MSE_READ_X_LOW #define MSE_READ_X_HIGH (busmouse.h) 0x23c 0x23d 0x23e 0x80 0xa0 (busmouse.c) outb(mse_read_y_low, MSE_CONTROL_PORT ); dy = (inb(mse_data_port) & 0xf); outb(mse_read_y_high, MSE_CONTROL_PORT); buttons = inb(mse_data_port); dy = (buttons & 0xf) << 4; buttons = ((buttons >> 5) & 0x07); 3 3

4 Assessment of Existing (Linux) Drivers Assembly-level programming style Macros unreadable code factorized, not suppressed no single programming style no typing / consistency checking The hardware interface code is: hard to read and maintain tedious and error prone 4 4

5 Lack of Support for the Driver Programmer Paper documentation» natural language» manufacturer-specific terminology» inconsistencies, ambiguities, omissions, typos Mixed levels of abstractions» communication mechanisms, data layout, semantics Inherent complexity of devices Laborious testing until expected functionality is obtained 5 5

6 Devil: a DEVice Interface Language Existing device interface code outb(mse_read_y_low, MSE_CONTROL_PORT ); dy = (inb(mse_data_port) & 0xf); outb(mse_read_y_high, MSE_CONTROL_PORT); buttons = inb(mse_data_port); dy = (buttons & 0xf) << 4; Application API System API Driver DI Device C Devil Generated Stubs DevIL 6 6

7 Our Vision High-level description of device interface Easy to write Strongly typed Consistency checking Code generation DevIL Hardware vendor, Public repository, Device expert Device Specification Verifier Compiler Functional interface Easy to use Debug/production mode Driver programmer Driver C Devil C stubs (run-time checks) 7 7

8 Devil: Key Concepts Ports communication point, address range Registers repository of data, granule of exchange Variables: programmer interface collection of register fragments semantic values:» bounded integers» enumerated types 8 8

9 Programmer Support: Verifying Critical Properties Consistency of Devil specifications no omission no double definition no overlapping type/size of variables C Devil interface usage in debug mode compile-time (type checking) run-time (assertion checking) 9 9

10 The Logitech Busmouse: functional interface dx (delta X) relative horizontal movement dy (delta Y) relative vertical movement buttons button state Read only variables! 10 10

11 Device Interface Code: C Devil vs. existing drivers dx = get_dx(); dy = get_dy(); buttons = get_buttons(); C Devil outb(mse_read_x_low, MSE_CONTROL_PORT); dx = (inb(mse_data_port) & 0xf); outb(mse_read_x_high, MSE_CONTROL_PORT); dx = (inb(mse_data_port) & 0xf) << 4; outb(mse_read_y_low, MSE_CONTROL_PORT ); dy = (inb(mse_data_port) & 0xf); outb(mse_read_y_high, MSE_CONTROL_PORT); buttons = inb(mse_data_port); dy = (buttons & 0xf) << 4; buttons = ((buttons >> 5) & 0x07); Existing code 11 11

12 The Logitech Busmouse: detailed description base + 2 base + 0 dx Direct register 0 index *.... Register array buttons dy 12 12

13 Direct registers base + 2 base + 0 dx fi index_reg 0 index *.... Register array buttons dy... register index_reg = write base@2, mask : bit[8]; 13 13

14 Private device variables base + 2 base + 0 dx fi index_reg 0 index *.... Register array buttons dy... register index_reg = write base@2, mask : bit[8]; private variable index = index_reg[6..5] : int(2); 14 14

15 Indexed registers base + 2 base + 0 dx index fi index_reg *.... fi x_low fi x_high fi y_low fi y_high buttons dy... register index_reg = write base@2, mask : bit[8]; private variable index = index_reg[6..5] : int(2);... register x_low = read base@0, pre {index = 0}, mask ****... : bit[8]; register x_high = read base@0, pre {index = 1}, mask ****... : bit[8];

16 ... register index_reg = write base@2, mask : bit[8]; private variable index = index_reg[6..5] : int(2);... register x_low = read base@0, pre {index = 0}, mask ****... : bit[8]; register x_high = read base@0, pre {index = 1}, mask ****... : bit[8];... variable dx = x_high[3..0] # x_low[3..0], volatile : signed int(8); variable dy = y_high[3..0] # y_low[3..0], volatile : signed int(8); base index Interface variables fi index_reg base *.... buttons dx fi x_low fi x_high fi y_low fi y_high dy 16 16

17 What About Performance? Sharing registers between variables may induce performance penalty additional I/O w.r.t. hand-crafted drivers command parameters Re-engineering of performance critical drivers IDE disk driver Permedia2 X11 driver 17 17

18 IDE Linux Driver (intel 82371SB) Characteristics: many initializations DMA/PIO-loop for transfer DMA mode C: 14 I/Os Devil: 20 I/Os Mb/s PIO-32bits mode, 16 sectors/interrupt C (rep loop): 8.17 Mb/s Devil (C loop): 7.36 Mb/s (90% of C) Devil (rep loop): 8.17 Mb/s 18 18

19 Permedia2 X11 driver Characteristics: registers mapped in memory buffered write (on-chip FIFO) same number of I/Os Screen copy operations (24 bpp) 100% performance of C Rectangle operations (24 bpp) 97%-100% performance of C difference due to stub code for small size operation 19 19

20 Benefits of Devil Expressivity» advanced Devil constructs (see paper and manual)» DMA, sound, interrupt, Ethernet controllers Guaranteed safety» Mutation-based experiment (typo simulation)» 5 times less prone to errors than C code Negligible performance overhead Improved productivity» reuse of specifications» tools and verifications 20 20

21 Our Vision (On-going work) Hardware vendor Device specification Device interface documentation Verifier Compiler Device interface implementation Driver programmer Device driver specification DSL type-checker DSL compiler DSL optimizer Generated device driver Device driver documentation 21 21

22 Conclusion Step toward the development of robust drivers Compiler/checker available No performance penalty Expressive enough to allow the specification of various devices Instance of our vision: DSL for Operating System Design 22 22

23 The details are in Devil 23 23

24 Questions? Specifications/compiler/manual available : Public CVS repository of specs Please contribute 24 24